Hemolytic uremic syndrome (HUS) is characterized by thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure. HUS is classified as one of two types: diarrheal-associated (D+ HUS; also referred to as shiga toxin producing E. coli (STEC)-HUS or typical HUS) and non-diarrheal or atypical HUS (aHUS). D+ HUS is the most common form, accounting for greater than 90% of cases and is caused by a preceding illness with a shiga-like toxin-producing bacterium, e.g., E. coli 0157:H7. aHUS is rare and has a mortality rate of up to 25%. Many patients with this disease will sustain permanent neurological or renal impairment, e.g., at least 50% of aHUS patients progress to end-stage renal failure (ESRF). See, e.g., Kavanagh et al. (2006) British Medical Bulletin 77 and 78:5-22.
aHUS can be genetic, acquired, or idiopathic. Hereditable forms of aHUS can be associated with mutations in a number of human complement components including, e.g., complement factor H (CFH), membrane cofactor protein (MCP), complement factor I (CFI), C4b-binding protein (C4BP), complement factor B (CFB), and complement component 3 (C3). See, e.g., Caprioli et al. (2006) Blood 108:1267-1279. Certain mutations in the gene encoding CD55, though not yet implicated in aHUS, are associated with the severity of aHUS. See, e.g., Esparza-Gordillo et al. (2005) Hum Mol Genet 14:703-712.
Until recently, treatment options for patients with aHUS were limited and often involved plasma infusion or plasma exchange. In some cases, aHUS patients undergo uni- or bilateral nephrectomy or renal transplantation (see Artz et al. (2003) Transplantation 76:821-826). However, recurrence of the disease in treated patients is common. Recently, treatment of aHUS patients with the drug Soliris® was approved in the United States of America and in Europe. Despite finally having a useful drug for treatment of aHUS patients, there is still a need to diagnose patients with aHUS, as well as monitor the progression and abatement of aHUS.